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Abrosexual flag colorpicked from dwarf galaxy Sextans A with polycyclic aromatic hydrocarbons
The Umbrella Galaxy NGC 4651
It's raining stars in NGC 4651, but the umbrella isn't stopping it, the umbrella is the stars.
What on the surface looks like a fairly normal spiral galaxy, has this 100,000 light years long arm with an arc at the outer edge. How did this get here ?
Just like our own galaxy, that has smaller dwarf galaxies orbiting around 150,000 light years out, this one appears to have suddenly merged with one, maybe due to gravitational interactions with other galaxies, or that the dwarf galaxy wasn't in a stable orbit and ultimately would have fallen in one way or another.
Eventually the stars will settle into a new home, but in the mean time, the galaxy will sport an umbrella for many more million years to come.
MIT researchers discover the universe’s oldest stars in our own galactic backyard
New Post has been published on https://thedigitalinsider.com/mit-researchers-discover-the-universes-oldest-stars-in-our-own-galactic-backyard/
MIT researchers discover the universe’s oldest stars in our own galactic backyard
MIT researchers, including several undergraduate students, have discovered three of the oldest stars in the universe, and they happen to live in our own galactic neighborhood.
The team spotted the stars in the Milky Way’s “halo” — the cloud of stars that envelopes the entire main galactic disk. Based on the team’s analysis, the three stars formed between 12 and 13 billion years ago, the time when the very first galaxies were taking shape.
The researchers have coined the stars “SASS,” for Small Accreted Stellar System stars, as they believe each star once belonged to its own small, primitive galaxy that was later absorbed by the larger but still growing Milky Way. Today, the three stars are all that are left of their respective galaxies. They circle the outskirts of the Milky Way, where the team suspects there may be more such ancient stellar survivors.
“These oldest stars should definitely be there, given what we know of galaxy formation,” says MIT professor of physics Anna Frebel. “They are part of our cosmic family tree. And we now have a new way to find them.”
As they uncover similar SASS stars, the researchers hope to use them as analogs of ultrafaint dwarf galaxies, which are thought to be some of the universe’s surviving first galaxies. Such galaxies are still intact today but are too distant and faint for astronomers to study in depth. As SASS stars may have once belonged to similarly primitive dwarf galaxies but are in the Milky Way and as such much closer, they could be an accessible key to understanding the evolution of ultrafaint dwarf galaxies.
“Now we can look for more analogs in the Milky Way, that are much brighter, and study their chemical evolution without having to chase these extremely faint stars,” Frebel says.
She and her colleagues have published their findings today in the Monthly Notices of the Royal Astronomical Society (MNRAS). The study’s co-authors are Mohammad Mardini, at Zarqa University, in Jordan; Hillary Andales ’23; and current MIT undergraduates Ananda Santos and Casey Fienberg.
Stellar frontier
The team’s discoveries grew out of a classroom concept. During the 2022 fall semester, Frebel launched a new course, 8.S30 (Observational Stellar Archaeology), in which students learned techniques for analyzing ancient stars and then applied those tools to stars that had never been studied before, to determine their origins.
“While most of our classes are taught from the ground up, this class immediately put us at the frontier of research in astrophysics,” Andales says.
The students worked from star data collected by Frebel over the years from the 6.5-meter Magellan-Clay telescope at the Las Campanas Observatory. She keeps hard copies of the data in a large binder in her office, which the students combed through to look for stars of interest.
In particular, they were searching ancient stars that formed soon after the Big Bang, which occurred 13.8 billion years ago. At this time, the universe was made mostly of hydrogen and helium and very low abundances of other chemical elements, such as strontium and barium. So, the students looked through Frebel’s binder for stars with spectra, or measurements of starlight, that indicated low abundances of strontium and barium.
Their search narrowed in on three stars that were originally observed by the Magellan telescope between 2013 and 2014. Astronomers never followed up on these particular stars to interpret their spectra and deduce their origins. They were, then, perfect candidates for the students in Frebel’s class.
The students learned how to characterize a star in order to prepare for the analysis of the spectra for each of the three stars. They were able to determine the chemical composition of each one with various stellar models. The intensity of a particular feature in the stellar spectrum, corresponding to a specific wavelength of light, corresponds to a particular abundance of a specific element.
After finalizing their analysis, the students were able to confidently conclude that the three stars did hold very low abundances of strontium, barium, and other elements such as iron, compared to their reference star — our own sun. In fact, one star contained less than 1/10,000 the amount of iron to helium compared to the sun today.
“It took a lot of hours staring at a computer, and a lot of debugging, frantically texting and emailing each other to figure this out,” Santos recalls. “It was a big learning curve, and a special experience.”
“On the run”
The stars’ low chemical abundance did hint that they originally formed 12 to 13 billion years ago. In fact, their low chemical signatures were similar to what astronomers had previously measured for some ancient, ultrafaint dwarf galaxies. Did the team’s stars originate in similar galaxies? And how did they come to be in the Milky Way?
On a hunch, the scientists checked out the stars’ orbital patterns and how they move across the sky. The three stars are in different locations throughout the Milky Way’s halo and are estimated to be about 30,000 light years from Earth. (For reference, the disk of the Milky Way spans 100,000 light years across.)
As they retraced each star’s motion about the galactic center using observations from the Gaia astrometric satellite, the team noticed a curious thing: Relative to most of the stars in the main disk, which move like cars on a racetrack, all three stars seemed to be going the wrong way. In astronomy, this is known as “retrograde motion” and is a tipoff that an object was once “accreted,” or drawn in from elsewhere.
“The only way you can have stars going the wrong way from the rest of the gang is if you threw them in the wrong way,” Frebel says.
The fact that these three stars were orbiting in completely different ways from the rest of the galactic disk and even the halo, combined with the fact that they held low chemical abundances, made a strong case that the stars were indeed ancient and once belonged to older, smaller dwarf galaxies that fell into the Milky Way at random angles and continued their stubborn trajectories billions of years later.
Frebel, curious as to whether retrograde motion was a feature of other ancient stars in the halo that astronomers previously analyzed, looked through the scientific literature and found 65 other stars, also with low strontium and barium abundances, that appeared to also be going against the galactic flow.
“Interestingly they’re all quite fast — hundreds of kilometers per second, going the wrong way,” Frebel says. “They’re on the run! We don’t know why that’s the case, but it was the piece to the puzzle that we needed, and that I didn’t quite anticipate when we started.”
The team is eager to search out other ancient SASS stars, and they now have a relatively simple recipe to do so: First, look for stars with low chemical abundances, and then track their orbital patterns for signs of retrograde motion. Of the more than 400 billion stars in the Milky Way, they anticipate that the method will turn up a small but significant number of the universe’s oldest stars.
Frebel plans to relaunch the class this fall, and looks back at that first course, and the three students who took their results through to publication, with admiration and gratitude.
“It’s been awesome to work with three women undergrads. That’s a first for me,” she says. “It’s really an example of the MIT way. We do. And whoever says, ‘I want to participate,’ they can do that, and good things happen.”
This research was supported, in part, by the National Science Foundation.
The Smallest Galaxies Have Off-Kilter Black Holes, But Astronomers Know Why
“Over 100 dwarf galaxies are now known to possess these black holes, with the first verified one discovered in 2011. However, solely finding radio emissions isn't enough: active black holes and star-formation bursts can create that signal. Researchers led by Dr. Amy Reines just conducted the first large-scale radio survey looking for black holes in dwarf galaxies. Using the Very Large Array, her team surveyed 111 dwarf galaxies, and found 13 of them that showed evidence for massive black holes. Remarkably, approximately half of the black holes were not located at the galaxy's centers, but were significantly off-kilter.”
When we examine the supermassive black holes we find in the Universe, they’re pretty much always found at the centers of galaxies. However, these are for black holes of millions-to-billions of solar masses and galaxies comparable in mass (or even greater than that) to the Milky Way. But dwarf galaxies, the majority of galaxies in the Universe, are predicted to have much smaller black holes. The first large survey of these galaxies was just undertaken, revealing a population of dwarf galaxies with black holes.
But half of them are located off-center, rather than at the center! Why is that? Astronomers know, and you can too!
(NASA/ESA) Hubble Steals a Look at a Hungry Giant
Text credit: ESA (European Space Agency), Image credit: ESA/NASA
NGC 1222, seen in this image taken with the Wide Field Camera 3 on board the NASA/ESA Hubble Space Telescope is a galaxy with a rather eventful story to tell. NGC 1222 has been described as a peculiar example of a type of galaxy known as a lenticular galaxy.
Astronomers think that NGC 1222 is in the process of swallowing up two much smaller dwarf galaxies that strayed too close to it. It is likely that the encounter was the trigger for the starburst in NGC 1222, bringing in fresh supplies of gas that are now fueling the burst of star formation.
I Zwicky 18
I Zwicky 18 is a dwarf galaxy located about 59 million light years away. The galaxy seems to be primarily composed of hydrogen and helium, lighter elements created in the Big Bang. Despite the galaxy’s age, it has a distinct lack of heavier elements.
I Zwicky 18 was once though to be a very young, nearby galaxy. It is only more recent research that has revealed its true age, some 1 to 10 billion years since the start of star formation, and its distance. Its few older stars are so faint they barely registered with Hubble. For some unknown reason, the galaxy has had an extremely low rate of star formation, leaving little evidence of its actual age.
Image and information from ESA.
Stellar Fireworks at the Rim
JWST has recently taken this amazing image of a star cluster with star's being born, but what's interesting here is, this isn't in the middle of a spiral arm, but rather right on the edges of our galaxy.
The stars were pictured in an area known as the Digel Clouds, some 26,000 light years from Earth, but a whopping 58,000 light years from the centre of our galaxy, making these stars very low in matellicity, and more similar to stars in dwarf galaxies than large spiral galaxies like our own.
What it shows is, star birth isn't just confined to where we expect it to be, it can and does happen in unexpected areas.
Stellar Steams in Intergalactic Space
It's easy to think that all stars exist neatly with a galaxy island, but the above montage shows a number of nearby large galaxies, and inverted to show the streams of stars that often stretch out 100's thousands of light years.
Cosmologists enjoy modelling the universe, and understanding how halo's and these star streams work help them create a better understanding and model of how galaxies evolve.
For example, I suspect you've not seen the above image representing our Milky Way, imagine if our Sun had been located in one of these streams, literally looking back at our own Milky Way, and a much darker sky at night.
Many of these steams are related to dwarf galaxies interacting and eventually being consumed by the main galaxy, it is the eventual fait of the Magellanic clouds, but has happened a number of times in the Milky Way's history.
Ultimately merger between larger galaxies ends up throwing out huge streams, unwound arms of galaxies that are stripped off as the mass of another galaxy beings to take hold, only to them move away leaving the arms outstretched, some of which may never return to the newly merged galaxy, while others eventually.
